Sliding anode magnetron sputtering source

ABSTRACT

A magnetron sputtering source includes a plurality of electrodes and a switching circuit. The switching circuit sequentially connects each of the plurality of electrodes to a ground reference, making it anodic, while connecting the remaining of the plurality of electrodes as cathodes. A method of operating the magnetron sputtering source includes steps of: providing a plurality of target arrangements; causing each of the plurality of target arrangements to act as a cathode; and sequentially causing each of the plurality of cathodes to temporarily act as an anode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/490,201, filed Jul. 25, 2003, hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a sputter deposition process for largearea thin film deposition, and more particularly to a magnetronsputtering source having one or more sliding anodes.

Sputter deposition is used in many applications for thin film depositionof various materials on various substrates. Large area coatings fordisplays, functional coatings (e.g. on architectural glass) or solarcells require a certain uniformity of the film-thickness over the wholesubstrate area.

Two basic approaches are known for performing sputter deposition.So-called “inline-processing” involves a substrate that is movedalongside a small coating source and is thereby coated with a respectivelayer. “Single substrate processing” involves coating the entiresubstrate “at once,” without moving either the source or substrateduring deposition. Single substrate processing is normally preferredsince it performs the sputter deposition more quickly. This normallyrequires a coating source that is equal to or larger than the size ofthe substrate. Such single, large cathodes, however, suffer from anincreasing non-uniformity with increasing substrate size due to physicallimitations.

For instance, increasing the glass-to-target distance too much can leadto layer problems. On the other hand, if the glass is too close to thetargets there will be a lack of electrons in the middle region of theglass, leading to poor layer uniformity.

To get more electrons to the middle of the glass without increasing theglass-to-target distance, greater anode surface area must be provided.To accomplish this, several approaches have been proposed.

One general approach involves providing an array of small cathodes invarious orders and arrangements, such as parallel bars, checker-boardpatterns, and the like. U.S. Pat. No. 6,093,293 to Haag et al.,incorporated herein by reference, describes an arrangement of severalbar-shaped targets mounted one alongside the other and separated byrespective slits. Each of the target arrangements includes a respectiveelectric pad to allow it to be operated electrically independently fromthe other target arrangement. Further, each target arrangement includesa controlled magnet arrangement generating a time-varying magnetronfield upon the target arrangement. Each of the magnet arrangements iscontrolled independently from the others.

Even such cathode arrays have size limitations, since it is impracticaland technically not feasible to raise the number of cathodes arbitrarilywith each upscale of the deposition system. Therefore, a furtherapproach for improving sputter deposition uniformity for largesubstrates is needed.

A major problem with increasing cathode size is a decrease of theelectrical field density in the center of the cathode. This decreaseresults in a lower plasma density and therefor in a lower depositionrate. To avoid this potential drop towards the center of the cathode, itis necessary to provide an anode near the center. Due to limited spacebetween the targets it is not possible to install permanent anodes withsufficient conductivity without raising the danger of arcing during thedeposition process.

SUMMARY OF THE INVENTION

According to the present invention, a magnetron sputtering sourcecomprises: a plurality of electrodes, and a switching circuit forsequentially connecting each of said plurality of electrodes to a groundreference and connecting the remaining of said plurality of electrodesas cathodes.

According to a further aspect of the present invention, a method ofoperating a magnetron sputtering source comprises steps of: providing aplurality of target arrangements; causing each of said plurality oftarget arrangements to act as a cathode; and sequentially causing eachof said plurality of cathodes to temporarily act as an anode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are schematic drawings showing a sliding anode sputteringsource arrangement at sequential points in time according an exampleembodiment of the present invention;

FIG. 2 is a timing diagram showing switching of cathodes to anodesaccording to an example embodiment of the present invention;

FIG. 3 is a schematic drawings showing a sliding anode sputtering sourcearrangement having hexagonal-shaped electrodes according to an exampleembodiment of the present invention;

FIG. 4 is a schematic drawings showing a sliding anode sputtering sourcearrangement having round electrodes according to an example embodimentof the present invention; and

FIG. 5 is a schematic drawings showing a sliding anode sputtering sourcearrangement having ring-shaped electrodes according to an exampleembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, in order to provide an anode in thevicinity of the cathode center, each of a set of electrodes havingtargets is alternating switched to ground during the sputtering process.In this way a homogeneous electrical field distribution is provided andthe uniformity of the deposited films over the whole area is improved.

As shown by way of example in FIGS. 1A, 1B, 1C and 1D, an array 10 ofspaced apart, bar-shaped target arrangements 12 a, 12 b, 12 c, 12 d, 12e, 12 f are provided. Each of the target arrangements 12 a-12 f isconnected as an electrode to a switching circuit 14. The switchingcircuit connects each of the target arrangements in “deposition mode” ascathodes and then, in sequential fashion, connects one or more of thetarget arrangements to a ground potential, causing them to temporarilyact as anodes, also referred to as “anode mode.”

In order to provide the optimal deposition conditions for differenttarget and substrate materials and for different system setups, severalparameters can be adjusted as necessary. According to the presentembodiment as shown in the timing diagram of FIG. 2, AS_(ON), the timefor a target to be switched to and kept in an anode state, can vary from1 to 300 milliseconds. Similarly, AS_(ON), a waiting time betweenswitching off one anode and switching on the next anode, can vary from 0to 500 milliseconds. Further, it is possible to choose which targetarrangements are switched to the anode state during deposition bysetting “ENABLE” equal to “YES” or “NO.” For example, for cathode #3,“ENABLE” is set to “NO,” and therefore cathode #3 will be skipped in theswitching sequence and always remain powered as a cathode. TS, indicatesthe starting target(s), indicating which target arrangement orarrangements will be switched to anode state when the switching circuitis started.

In laboratory tests, we have observed an improvement of the thicknessnon-uniformity from 15%, without using the sliding anode arrangement, to5% using the sliding anode of the present invention. Conditions wereidentical in all other respects. The test sliding anode arrangement hadthe following settings: ASOn=5 ms;ASOƒƒ=0 ms; enable =“yes” for middletarget arrangements #2 to #9; TS =#3 and #7.

Although FIG. 2 shows one example embodiment of the present invention,it is contemplated that other “patterns” of switch-modes may beachieved, for example using one cathode temporarily as anode, or usingmore than two cathodes at the same time. Further, an overlapping modecould be realized, wherein while a first anode is present and active, asecond anode is being switched two ground, after which the first anodereturns to deposition mode as a third anode is being connected toground.

Further, although FIGS. 1A-1D. show bar-shaped target arrangements in aspaced-apart, parallel array, other target shapes and arrayconfigurations have been contemplated. For example, a checker-board likecathode arrangement may be provided, using analogous switching patterns.Similarly, as shown by way of example in FIGS. 3-5 the target electrodesof the present invention can have other shapes and arrangements, such asround, ring-shaped, polygon-shaped, or the like, to be grouped inchecker-board, honeycomb or other suitable arrangements. FIG. 3 shows anarray of hexagonal shaped electrodes 12′ in a honeycomb arrangement.FIG. 4 shows an array of round electrodes 12″ in a checkerboard pattern.FIG. 5 shows an array of ring-shaped electrodes 12′″.

Although not shown in detail herein, according to the presentembodiment, the switching circuit comprises insulated-gate bipolartransistors (IGBT) as switching elements. IGBT's can be operate with thehigh cut-off voltages or reverse voltages and provide the large amountsof current necessary for sputter deposition. For example, IGBT's arecommercially available that can be operated, by means of a pulsed powersupply (e.g. a commercially available “Pinnacle Plus” power supply) with1700 volts and a nominal current 100 Amps. Field effect transistors(FET) with similar properties are available up to 1500 Volts, but arenot as readily available. Further, these FET's are loadable only up toabout 12 amps and therefore several FET's would have to be connected inparallel to switch the amount of current necessary for sputterdeposition.

Depending on the number of the target arrangements, and as mentionedabove, individual target arrangements or several target arrangementscould be connected to ground at one time. The more target arrangementsthat serve as anodes, the more the effective target area that isavailable, by increasing plasma density. However, the deposition ratedecreases as additional target arrangements are used as anodes, sinceless cathodic target arrangements are operating at once. It is thereforereasonable, to use as few target arrangements as possible as anode.

In the present embodiment, the switching of target arrangements iscontrolled flexibly, by a programmable controller. In another embodimentof the invention, the outermost cathodes are not switched, but insteadwould be operated at a constant higher power to compensate for edgeeffects.

Further, depending on the capabilities of the power source utilized, theswitching may be realized by respective clocking of the control system.As a further alternative, the cathodes may be directly connected toground, without first disconnecting the power, in order to achieveshorter cycle times.

It should be evident that this disclosure is by way of example and thatvarious changes may be made by adding, modifying or eliminating detailswithout departing from the fair scope of the teaching contained in thisdisclosure. The invention is therefore not limited to particular detailsof this disclosure except to the extent that the following claims arenecessarily so limited.

1. A magnetron sputtering source comprising: a plurality of electrodes;and a switching circuit for sequentially connecting each of saidplurality of electrodes as an anode and connecting the remaining of saidplurality of electrodes as cathodes, wherein the switching circuitprovides a delay after disconnecting any of said plurality of electrodesfrom a ground reference before connecting any other one of saidplurality of electrodes to the ground reference, and wherein during thedelay none of said plurality of electrodes acts as an anode and at leastone of said plurality of electrodes acts as a cathode.
 2. The magnetronsputtering source of claim 1, wherein each of said plurality ofelectrodes is a bar-shaped target.
 3. The magnetron sputtering source ofclaim 1, wherein each of said plurality of electrodes is one of a roundtarget, a ring-shaped target and a polygon-shaped target.
 4. Themagnetron sputtering source of claim 1, wherein the switching circuitkeeps each of said plurality of electrodes connected to the groundreference for less than 300 milliseconds.
 5. The magnetron sputteringsource of claim 1, wherein the delay is less than 500 milliseconds. 6.The magnetron sputtering source of claim 1, wherein said switchingcircuit comprises an insulated gate bipolar transistor.
 7. The magnetronsputtering source of claim 1, wherein said switching circuitsimultaneously connects a plurality of said plurality of electrodes tosaid ground reference.
 8. The magnetron sputtering source of claim 1,wherein said switching circuit comprises an electrode switching selectorfor selecting said plurality of electrodes from an array of electrodesto be switched by said switching circuit.
 9. The magnetron sputteringsource of claim 1, wherein said plurality of electrodes are selectedfrom an ray of electrodes and wherein electrode located at an outsideperiphery of said array of electrodes are excluded from said pluralityof electrodes.
 10. The magnetron sputtering source of claim 1, whereinduring the sequentially connecting, one of said plurality of electrodesalways remains powered as a cathode.
 11. A method of operating amagnetron sputtering source comprising steps of: providing a pluralityof target arrangements; causing each of said plurality of targetarrangements to act as a cathode; and sequentially causing each of saidplurality of target arrangements to temporarily act as an anode for apredetermined on-time by connecting each of said plurality of targetarrangements to a ground reference, wherein after disconnecting any ofsaid plurality of target arrangements from the ground reference a delayis provided for before connecting any other one of said plurality oftarget arrangements to the ground reference, and wherein during thedelay none of said plurality of target arrangements acts as an anode andat least one of said plurality of electrodes acts as a cathode.
 12. Themethod of operating a magnetron sputtering source of claim 11, whereineach of said plurality of target arrangements is kept as an anode forless than 300 milliseconds.
 13. The method of operating a magnetronsputtering source of claim 11, wherein said predetermined on-time isless than 300 milliseconds.
 14. The method of operating a magnetronsputtering source of claim 11, further comprising a step of: after thedelay for a predetermined off-time causing said any other one of saidplurality of target arrangements to temporarily act as an anode.
 15. Themethod of operating a magnetron sputtering source of claim 14, whereinsaid predetermined off-time is less than 500 milliseconds.
 16. Themethod of operating a magnetron sputtering source of claim 14, whereinduring the sequentially causing step, one of said plurality ofelectrodes always remains powered as a cathode.